By Mathilda Gustafsson and Rashmi Bopitiya
8 April 2024
Although oysters are living creatures, and thereby classified as an animal source food, they do not possess a central nervous system and are therefore not believed to be sentient, meaning they are not receptive to pain. As a result, some of the people that turn to veganism for reasons regarding animal welfare make an exception for oysters and other molluscs knowing that they ultimately don’t feel anything.
By strict definition, oysters don’t classify as plants. Yet, some vegans do make an exception for their consumption. Why might this be so? Is eating oysters and other bivalves a culinary culture worth promoting? To delve into these questions, we interviewed Emeritus Prof. Dr. Aad Smaal, a retired professor of sustainable shellfish culture at Wageningen University, whose expertise lies in the role of shellfish in ecosystems.
A Vegan’s Raison d'être
Understanding why vegans may indulge in mollusk consumption requires exploring their core principles. Typically, vegans advocate for plant-based diets due to concerns about health, sustainability, and animal welfare. It’s within this framework that exceptions for oysters can be rationalized:
Oysters…
…are a healthy source of protein, rich in unsaturated fatty acids that are good for the brain;
…are low trophic aquaculture whose cultivation is nearly identical to the natural process and are thus argued for being the most sustainable source of protein;
…have a positive impact on biodiversity by recycling nutrients (ie., nitrogen and carbon) and increased phytoplankton turnover that prevent massive algal blooms and strengthen stability of the ecosystem
…accumulate to form beds that are good habitats for biodiversity, even cultivated sites, especially bottom culture. This is true for mussels but the similar effects are predicted for oyster beds;
…are invertebrates, meaning that they lack a spinal cord and a central nervous system. Essentially, they don’t feel pain the way we do.
These arguments, supported by scientific research, position bivalves as a healthy, sustainable, and ethically acceptable protein source. To what extent are these arguments true? Better yet, are these truly the core reasons for vegan mollusk consumption?
Cruelty-free Consumption
Central to vegan ethics is cruelty-free consumption. The absence of a central nervous system in oysters aligns with this principle. However, the question of whether bivalves experience pain remains unresolved. Most, if not all, invertebrates have the capacity to detect and respond to stimuli. Although their nervous system is much simpler in composition than various other species, mollusks do have a nervous system. They also have what some might call their equivalent of the brain - a ganglia - which is what enables their systems to function in the way they are supposed to. It is difficult to infer pain in other species as we all have different parameters by which we experience and respond to such stimuli. We therefore cannot apply the same guidelines of pain that we do to ourselves, but nor should we reduce them to mere disembodied vessels.
Dr. Smaal highlights the challenges in assessing pain in these organisms: given the lack of a central nervous system, a proxy for pain is required. With fish, a proxy to pain is stress levels. Researchers look for stress hormones and how they change based on the handling of the animal. Similar research can be conducted on mussels. However, this is easier said than done. For bivalves, assessing pain is a difficult thing, especially when trying to compare stress induced from human handling against natural conditions: will an oyster or a mussel feel more stress when eaten by a bird in nature or prepared by a human for consumption? This brings to question whether the argument of cruelty-free consumption is relevant to the choice of eating oysters.
A Sustainability Icon
Aside from being a healthy source of unsaturated fatty acids, oysters are also considered one of the most sustainable meat sources. Shellfish aquaculture has been shown to promote the growth of biodiversity in underwater ecosystems. These habitat defenders help keep the sea clean by a process known as filter-feeding, whereby large volumes of water is pumped through their bodies to remove “algae, organic matter, excess nutrients,” etc (NOAA Fisheries, 2022). “One adult oyster can filter up to 50 gallons of water each day” (NOAA Fisheries, 2022). Eventually, when the oysters are harvested, the excess nitrogen and phosphorus stored within their shells are removed from the ecosystem, improving algal bloom and oxygen levels to ultimately mitigate habitat loss. This is why oyster farms are considered much more environmentally friendly than their wild counterparts, and certainly more than fish farms.
When asked about why oysters are considered a sustainable meat source, Dr. Smaal first corrected the word ‘meat’ for ‘protein’ reasoning that, “In terms of food transition, we need to transition to more sustainable protein sources”. When answering the question, he mentioned how the positive returns to biodiversity from oyster cultivation has not yet been empirically proven (although it has for mussel cultivation). However, a few key factors to consider when discussing improvements to biodiversity with oyster culture are:
Type of cultivation (ex., bottom cultivation vs. long-line/ table cultivation);
Site-specific energy levels (ex., low-energy sites - sites with less water currents - lead to shell accumulation);
On-site disturbance: dredging in cultivated plots is quite high, leading to much more disturbance than in wild plots. This may result in biodiversity in a cultivated oyster plot being lower than a reference wild plot. However, with mussel plots, the opposite is true. Wild mussel beds survive in areas with lower predation due to freshwater flows, while culture plots are grown in more saline conditions near the sea. Freshwater chases starfish and other predators away and these more saline environments promote more biodiversity.
Oysters: A Sensual Aesthetic
Many speculations can be made as to why vegans make an exception for oysters, however market research highlights a very crucial other factor that needs to be taken into account.
Dr. Smaal's research delves into the cultural and aesthetic dimensions of oyster cuisine, shedding light on its timeless appeal. The reasons for eating oysters normally don’t include sustainability, but rather the festive atmosphere associated with eating shellfish. The cultural connotations of summer and special occasions is a driving force for oyster cuisine. In fact, Dr. Smaal, alongside nearly 100 authors, wrote a book about this very topic, the online version is linked below. “The magic of oysters is that it’s not clear what the magic is”, said Dr. Smaal, “Some arguments for its sensuality can be made because it’s hard outside and soft inside…[there are] many associations too with aphrodisiacs and libido. A study I did on mice showed how mice fed with oysters regularly were more sexually active than the control groups”. He went on to describe the special culture surrounding oyster consumption through the ages. For example, oysters were eaten in high quantities by the Romans and better yet, mythical stories depict Aphrodite landing on Cyprus in an oyster shell. All of this goes to show the rich culture surrounding oysters that is undoubtedly a strong force - if not, the strongest - driving their consumption.
All in all, the same criteria for why vegans opt to eat plants can apply for bivalves.
LINK TO BOOK: Goods and Services of Marine Bivalves
Works Cited